India, Dec. 14 -- A thick blanket of smog choked Delhi on Sunday, keeping air quality in the 'severe plus' category a day after authorities imposed stage 4 curbs under the Graded Response Action Plan (GRAP), with the capital's 24-hour average air quality index (AQI) recorded at 460 at 8 am.

It was 431 at 4 pm on Saturday. Authorities had announced GRAP stage 3 on Saturday morning after the AQI crossed 400. Stage 4 curbs were put in force following an emergency meeting convened in the evening, citing a rising trend in the AQI.

Forecasts show no immediate relief is in sight, with the AQI set to stay severe throughout Sunday. It may marginally improve to 'very poor' on Monday, the Early Warning System for Delhi (EWS) said.

At 8 am, all 39...